The present invention relates to manipulating video signals in the form of a composite encoded signals, such as digitized PAL or NTSC etc encoded according to the D2 standard.
A video graphics system is disclosed in U.S. Pat. No. 4514818, assigned to the present Assignee and included herein as part of the present disclosure, in which a video image is viewed on a monitor by generating an analogue video signal from digitally stored image data. The image data may be modified by the operation of a stylus upon a touch tablet, in which movement of the stylus simulates the operation of a graphic implement such as a paintbrush, chalk or an airbrush. A machine embodying the techniques disclosed in the aforesaid patent is manufactured by the present Assignee and sold under the trade mark "PAINTBOX".
Video graphics systems are often used during the post production stages of video making, in which a clip of video is manipulated by the system (frame by frame) so that elements may be added or removed from a live action shot, or animated sequences generated. The original recordings are often in the form of composite signals, such as PAL or NTSC, which are termed composites because they may be transmitted over a single channel, the chrominance signal (hue and saturation) being frequency multiplexed above the luminance signal. However, to allow manipulation by a video graphics system, the frames must be decoded into separate components, with a baseband signal for each of the three primary colours of red, green and blue, or for each of a luminance and two colour difference signals. If so required, the component signals may be re-coded back into composite form after manipulation.
A problem which results from decoding between composite video (say PAL) and component video is that clips which undergo this process do not match perfectly with unprocessed clips. A possible solution would be to perform the decoding and re-encoding process on all of the video clips as part of the editing process, however, this is not only time consuming but also unnecessary degradation to the whole of the production.